Typically, solid oxide fuel cells (SOFC) employ an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (MEA). The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, generally, predetermined numbers of the separators and the electrolyte electrode assemblies are stacked together to form a fuel cell stack.
In the fuel cell, a fuel gas such as a hydrogen gas and an oxygen-containing gas such as the air need to be supplied to the anode and the cathode of the electrolyte electrode assembly, respectively. Further, improvement in the current collection efficiency needs to be achieved.
In a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2004-522285 (PCT), as shown in FIG. 23, a fuel cell plate 1a and a gas separator plate 2a are stacked together. Each of the fuel cell plate 1a and the gas separator plate 2a has a circular shape. In the fuel cell plate 1a, a cathode layer 4a and an anode layer 5a are formed on both surfaces of an electrolyte layer 3a. Electrically-conductive passages 7a passing through an electrode-contacting zone 6a are formed in the gas separator plate 2a. The electrically-conductive passages 7a are made of silver or silver based material as electrically conductive material.
Further, in a solid oxide fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2002-237312, as shown in FIG. 24, a power generation cell 1b, and a pair of metal separators 2b for supplying a fuel gas to a fuel electrode layer and an oxygen-containing gas to an air electrode layer are provided. A fuel electrode current collector 3b is interposed between a fuel electrode layer of the power generation cell 1b and one of the metal separators 2b, and an air electrode current collector 4b is interposed between the air electrode layer of the power generation cell 1b and the other of the metal separators 2b. The metal separator 2b is plated with silver or silver alloy. Further, the air electrode current collector 4b is made of porous material containing silver or silver alloy, or porous material formed by coating porous material containing silver or metal other than silver with silver or silver alloy.
Further, in a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2006-253071, as shown in FIG. 25, a fuel electrode 1c made of porous material, an electrolyte membrane 2c provided on one of front and back surfaces of the fuel electrode 1c, an air electrode membrane 3c formed on the electrolyte membrane 2c, air flow passages 4c having grooves formed in a matrix pattern on the other surface of the fuel electrode 1c for supplying the air to the air electrode membrane 3c of the adjacent fuel cell, an interconnector membrane 5c formed on the surface having the air flow passages 4c are provided. The fuel electrode 1c has a plurality of fuel gas flow passages 6c. 